Previous safety systems in vehicles include a multi-stage monitoring component, called a watchdog. In this connection, a differentiation may be made between hardware and software watchdogs.
In a first stage, a watchdog monitors the frequency of the system timer, which a microprocessor (μC) derived by, for example, frequency division from its own interface timer, synchronously provides to additional internal or external, electrical, electronic or digital modules.
In further stages, “queries” of the watchdog to the microprocessor must be answered correctly. Queries may be understood to be, for example, requests as well as certain arithmetic tasks. The microprocessor resources necessary for answering the queries may be assembled individually, in particular, from the microprocessor functions used in the application in the corresponding program level. The programming of the watchdog request further ensures that the queries may only be responded to correctly if the application program sequence is correct. Watchdog stages must therefore be configured for each program level (real time program, background program, etc.).
In a more stringent variant, the correct responses of the microprocessor to the individual watchdog stages (real time program, background program, etc.) must be given within a predefined time window.
Systems which must make decisions very quickly, i.e., in particular in less than 2 milliseconds, for example, systems for activating a passenger protection arrangement for a vehicle, must detect errors which result in a malfunction (i.e., for example, unintentional triggering of the passenger protection arrangement) in good time. This occurs today using frequency monitoring of the system timer of the microprocessor with the aid of a watchdog. As a result of this, each defect of the oscillator in the microprocessor is detected. In this case, the oscillator may be present in the form of a quartz or resonator.